The preparation of sodium bicarbonate and ammonium sulfate has been discussed at length in the prior art. One of the most recent patents regarding this technology is U.S. Pat. No. 6,106,796, issued to Phinney, Aug. 22, 2000. This patent effectively demonstrates the fact that in all of the prior art, the ability to produce a non contaminated ammonium sulfate product does not exist. This patent is effective for synthesizing high quality ammonium sulfate and sodium bicarbonate by progressive precipitation. This sequencing of precipitations results in “partitioned decontamination” by continuously removing contamination from a predecessor solution which has already been exposed to purification.
Canadian Patent No. 2,032,627, issued Jan. 14, 1997 to Thompson et. al., teaches yet another process for producing sodium carbonate and ammonium sulfate from naturally occurring sodium sulfate. The reference is concerned with the preparation of a double salt of sodium and ammonium sulfate. This is a source of contamination when one is trying to form reasonably pure ammonium sulfate and the presence of any double salt and sodium in an ammonium sulfate product does nothing other than reduce the value of the ammonium sulfate to a non-commercial product. In the methodology, it is clearly stated on page 13, beginning at line 8:                “ . . . the brine remaining after screening off the solid sodium bicarbonate contains a mixture of unreacted sodium sulfate, ammonium sulfate, ammonium bicarbonate and minor amounts of sodium bicarbonate. This brine is transferred by a pump 36 into a gas recovery boiler 31 where it is heated to a temperature of 95° to 100° C. Under these conditions, the ammonium bicarbonate breaks down and sodium bicarbonate dissolved in the brine reacts with ammonium sulfate to produce sodium sulfate, carbon dioxide and ammonia. Carbon dioxide and ammonia dissolved in the brine boil off, leaving in the solution a mixture composed mostly of sodium and ammonium sulfate The carbon dioxide and ammonia so regenerated are cooled in a gas cooler 32 and returned to the reactor 21 by a blower 33 after being further cooled in a gas cooler 34. This regeneration step minimizes the amount of carbon dioxide and ammonia used in the process.”        
It is clear that the brine is evaporated and that the ammonium sulfate is reacted with the brine to produce sodium sulfate inter alia. The phase equilibria relationship between the elements present in the system was not recognized.
The teachings of this reference provide for a closed loop system for a sodium sulfate and ammonium sulfate saturated solution system. This system results in the formation of double salt. The teachings are limited in that it was believed that the solubility difference could yield an ammonium sulfate product. This is incorrect; the result is an ammonium sulfate contaminated system.
In Stiers et al, U.S. Pat. No. 3,493,329, the teachings are directed to the preparation of sodium bicarbonate and hydrochloric acid. This goal is consistent with the teachings of Stiers et al. at column 11 of the disclosure beginning at line 23 through line 43, wherein the following is indicated:                “If, instead of precipitating the double salt in the first stage of the process, it is preferred to precipitate ammonium sulfate, the following procedure may be adopted.        Referring now to FIG. 10, it will be seen that each of the three curves which divide this figure into three parts corresponds to the simultaneous precipitation of two salts.        At any given temperature, the point representing a system may be vertically displaced by removing some of the water from the solution. In order to precipitate ammonium sulfate instead of the double salt, it is necessary to operate at a temperature greater than that at the triple point, i.e., about 59° C.        The point A, which corresponds to about 63° C. is suitable, since it is sufficiently distant from the triple point to avoid unwanted precipitation of the double salt without requiring too much heat.        It is clear that at the point A, there is simultaneous precipitation of sodium sulfate and ammonium sulfate, but this is in the form of a mixture of the two salts rather than as a double salt.”        
The teachings of the Stiers et al. reference not only are insufficient to direct one to formulate ammonium sulfate in a purity of greater than 75%, but the disclosure is further completely absent of any teaching on how to obtain ammonium sulfate singly. The Stiers et al. reference does not and can not result in the generation of ammonium sulfate as a single product as is clearly possible by the teachings of the present invention.
By following the Stiers et al. methodology, one cannot generate a pure ammonium sulfate product, since the reference does not recognize the limitations of the phase equilibria of the salt system and the combination of steps necessary to overcome the inherent contaminating steps associated with this salt system. Although there is a reference to point A in FIG. 10 of Stiers et al. for the preparation of the product, it is clear that although no double salt is indicated to be in the mixture, there is no indication that the product does not include mixed salt. This is reflected in the disclosure where Stiers et al. indicates that there is simultaneous precipitation of sodium sulfate and ammonium sulfate. This is consistent with the data that Stiers et al. provides as indicated at column 12 beginning at line 21. There is no data presented where the quantity of ammonium sulfate, standing on its own, is set forth. In each case, the data presented is expressed as a proportion precipitated in a compound, i.e, combined salt inter alia. Finally, from the text set forth beginning at line 32, Stiers et al. indicates that:                “ . . . From the foregoing it will be seen that the process according to the invention may be carried out by precipitating the ammonium sulfate in the form of the double salt, or as (NH4)2SO4 simultaneously with sodium sulfate, or by precipitating it simultaneously in the form of ammonium sulfate and in the form of the double salt.”        
From a review of FIGS. 10 and 11 (in Stiers et. al.), the fact that no ammonium sulfate is generated singly becomes evident. No data is presented for ammonium sulfate generation; the results from practicing this methodology are only a mixed salt and a double salt. Nothing else is obtainable by practicing this method.
Finally, Kresnyak et al. in U.S. Pat. No. 5,830,442, issued Nov. 3, 1998, teach an improved process for producing ammonium sulfate. This process is attractive where energy consumption and conversion efficiency are not of primary concern. In this process, sodium sulfate is removed by significant energy input to the evaporators with subsequent cooling. The result is a 2:1 ratio of double salt to solution which then must be evaporated in order to recover ammonium sulfate.
In view of the limitations of the prior art, it is evident that a need remains for a process whereby ammonium sulfate and sodium bicarbonate can be formulated in high yield at a high purity using commercially viable, energy efficient unit operations in the proper sequence. The present invention fulfills these objectives in an elegant manner.